I think maybe one of my favorite things about Disneyland is that even w/ things changing is there are still enough classic attractions in the park to take me back to being a kid. I have a grandmother w/alzheimer's, so i doubly enjoy the nostalgia burst because I want to enjoy my memories while I know I can, just in case.
The bell at the train station at main Street USA, along w/ the "Now boarding...." spiel.
The old man on the porch and banjo music in the Blue Bayou
The talking skull and "dead men tell no tales" in Pirates
"Hurry back......" when leaving the Haunted Mansion
There are countless others, but for me, those are the ones that instantly conjure up memories of being a 5 or 6 year old with my parents at the park.